In order to reduce exhaust emission, an internal combustion engine is provided with an exhaust gas recirculation (EGR) apparatus. The EGR apparatus has an EGR valve disposed in an EGR passage. The EGR valve adjusts quantity of EGR gas recirculating into an intake pipe through the EGR passage.
For example, Japanese patent No. 2560777 discloses an internal combustion engine having an EGR apparatus. An oxygen sensor is provided in an intake pipe. Based on output signals of the oxygen sensor, an opening degree of the EGR valve of when the EGR gas starts to recirculate is detected. Further, JP-2001-82260A discloses an internal combustion engine having an EGR apparatus in which an intake pressure sensor is provided in the intake pipe to detect an intake pressure. Based on the detected intake pressure, an opening degree of the EGR valve of when the EGR gas starts to recirculate is learned.
Especially, in a gasoline engine, since a sensitivity of combustion stability relative to an EGR gas quantity is relatively high, it is necessary to control the EGR gas quantity with high accuracy. When the exhaust gas recirculation is stopped, it is necessary for the EGR valve to accurately fully close the EGR passage to avoid an EGR gas leakage. Thus, it is necessary to accurately learn a full close position of the EGR valve.